Percevoir = ‘Perceive’ as in ‘I perceive footsteps in the distance.’ = ‘Je perçois des (bruits de) pas au loin.’

Se percevoir = ‘Perceive oneself’ as in ‘I don’t perceive myself as being fat.’ = ‘Je ne me perçois pas comme quelqu’un de gros.’

Apercevoir = ‘Seeing something/someone in an unaccurate manner’ as in ‘I (barely) saw her as she was away.’ = ‘Je l’ai aperçue alors qu’elle s’en allait.’

S’apercevoir = ‘Realize’ as in ‘I realized I didn’t have my cellphone.’ = ‘Je me suis aperçu que je n’avais pas mon téléphone portable.’

It should be noted that “S’apercevoir” can also be used as “Apercevoir” towards oneself, as in “Je me suis aperçu dans le mirroir.” = “I saw myself in the mirror.”